Australia's Great Barrier Reef is at risk because authorities are failing to protect the marine park by approving the dumping of dredge spoil, a former government official says.

Jon Day, who was a former director of Conservation Biodiversity and World Heritage at the Great Barrier Reef Marine Park Authority, says the dumping of dredge spoil will put more pressure on a reef that is already in decline.

The authority approved plans in January to dump three million cubic metres of dredge spoil at the Great Barrier Reef to expand Queensland's Abbot Point coal port.

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Australia's Great Barrier Reef is at risk because authorities are failing to protect the marine park by approving the dumping of dredge spoil from Abbot Point coal port, a former government official says

It's a decision that should not have been made, according to Mr Day, and is part of an ABC Four Corners investigation on Monday.

Scientists and senior officials within the authority faced a tense year-long struggle against the proposal, with fears about the effect the spoil could have on the marine park.

'The big question is why was it allowed to be approved,' Four Corners reporter Marian Wilkinson told Daily Mail Australia.

'The official view from the Environment Minister (Greg Hunt) is that they've put tougher environmental conditions on so they believe it can be done safely. But there's a lot of questions among experts inside and outside the agency about it.'

Jon Day, who was a former director of Conservation Biodiversity and World Heritage at the Great Barrier Reef Marine Park Authority, told ABC reporter Marian Wilkinson the dumping of dredge spoil would put more pressure on a reef that is already in decline

Mr Day, who resigned from the authority last month, says alternatives to sea dumping for Abbot Point weren't properly considered.

'If we take that into account and if we did a proper evaluation of all the alternatives, that decision would not have been made,' he said.

'Our own legislative mandate says "the long-term protection and conservation of the values", and we're not doing that.'

Wilkinson said the decision was criticised by UNESCO's World Heritage Committee, which will decide next year whether the reef should be declared 'in danger'.

The authority approved plans in January to dump three million cubic metres of dredge spoil at the Great Barrier Reef to expand Queensland's Abbot Point coal port

Reporter Marian Wilkinson Wilkinson said the decision was criticised by UNESCO's World Heritage Committee, which will decide next year whether the reef should be declared 'in danger'

'The other options to look at were trying to find a place to dump on land and trying to do something to extend the port's trestles so that ships didn't have to come so close to the reef,' Wilkinson said.

Mr Hunt, the federal environment minister who approved the dumping, told the program that Abbot Point was a 'line in the sand' and he has guaranteed that no further dumping will take place in the marine park under his watch.

'Of course, the argument from some of the scientists is why did we have to have this one in the first place?' Wilkinson said.